A milling technique known as high feed milling or HFM is characterized by a low engagement into a workpiece, in axial direction relative to a tool axis, and a high feed rate. The high speed milling machining method is widespread in industry. There are many cutting geometries which allow realizing this technique. Some geometries can be observed on solid tools and replaceable solid heads and others have been realized with different cutters having indexable cutting inserts mounted therein.
Ramping or a ramp down milling is known as a milling process with a lateral feed combining an axial feed. Due to the ability to achieve high metal removal rate in rough milling with relatively light machine tools the mentioned technique is very popular in the die and mold industry. Machining cavities and pockets is a typical application in this field, therefore, the tool ramping capabilities have significant meaning. Another important factor for the die and mold industry, namely, machining with a large tool overhang, which decreased static and dynamic stiffness of the clamped tool and affects cutting stability, requires reliable insert clamping in order to prevent premature insert wear and even its breakage.
There are two main design approaches to cutting edges of the tools for high feed milling, particularly for ramping. According to one approach the cutting edge is a portion of a cutter with round inserts of large diameter. According to another approach the cutting edge is a straight line inclined at a small angle. An high feed milling insert is clamped by a clamping screw that passes through the central hole of the insert, but in many cases an additional clamping element, like a clamping arm, is introduced in the tool design in order to reliably fix the insert into the pocket.
An example of a tool for high feed milling is described in U.S. Pat. No. 6,413,023 being directed to a product named HITACHI ASR Alpha Turbo line. The insert has a main cutting edge portion, a peripheral cutting edge portion and an internal straight cutting edge portion. The insert has a positive side inclination, that is, the side surfaces are forming with the upper surface an angle that is less than 90°. The patent figures show that the insert can have two or three cutting edges. The tool comprises two clamping elements. A first clamping element is the insert clamping screw. The second clamping element is the clamping arm.
FIGS. 1 and 2 show an example of a cutting insert with a positive geometry or, as mentioned above, a positive side inclination. FIG. 1 shows a general perspective view of a cutting insert of such a kind. FIG. 2 shows a cross section of the cutting insert of FIG. 1 taken along line II-II in FIG. 1. As clearly seen in FIG. 2, the side surfaces of the cutting insert form with the upper surface an angle that is less than 90°.
A similar approach to insert clamping is observed in DIJET High Feed Diemaster “SKS” Type, MITSUBISHI High-feed radius milling cutter AJX type (Japanese patent applications JP20040268123 20040915, JP20040259472 20040907), KORLOY HRM Tools. The inserts have three cutting edges and side inclination between 13° to 15° that ensures necessary relief for inserts mounted on a tool. As a result of the positive side inclination one of the components F1 of the pocket wall reaction force F tends to push the insert off from the pocket bottom, like shown for example in FIG. 3.
The clamping arm, an important element for rigid clamping and, hence, stable cutting, comprises a number of parts, and thus can cause a certain amount of inconvenience for an operator due to the necessity to use two different wrenches for insert indexing or replacing, namely, one for the clamping screw and the other for the clamping arm. Another disadvantage of using a clamping arm is the increased time necessary for the tool production, since there are more machining and assembling operations.
Furthermore, the clamping arm is an obstacle for free chip flow and experiences additional loading because of chip strikes, especially in pockets machining, when chip evacuation is difficult.
Therefore, some known solutions for HFM inserts with positive side inclination use a clamping screw only. For example, FETTE MultiEdge 3Feed, ISCAR FeedMill (U.S. Pat. No. 6,709,205) or SAFETY PENTA High Feed. FETTE (MultiEdge 3Feed) decreases the side inclination angle to 11°. ISCAR (FeedMill) adds a cylindrical protrusion to the insert bottom and a recess to the pocket base wall accordingly. The protrusion makes the location and clamping of the insert more reliable by the additional abutment surface but limits the number of indexable cutting edges since the cutting insert can not be reversible. All the indexable milling inserts considered above are one-sided.
U.S. Pat. No. 3,289,271 discloses a replaceable indexable cutting insert that is used for turning applications. The cutting insert is provided with a plurality of sides between two parallel faces such that each side has an angle less than 90° with another face. In FIG. 1 there is shown a cutting insert (10) with a generally trigonal shape, wherein the cutting insert utilizes on a given face (12) three cutting edges (40, 44, 48) that their sides (16, 20, 24) have less than 90° with the face (12).
Since the cutting insert (10) has three cutting edges per face, and since it is capable of being turned over to the other face, the cutting insert is provided with a total of six cutting edges. The cutting insert (10) is limited from being used for high speed machining since it is not provided with adequate means for disposing of chips, especially, for external milling together with ramp down milling.
It is the object of the present invention to provide a cutting insert that significantly reduces or overcomes the aforementioned disadvantages.
It is a further object of the present invention to provide a cutting insert that is particularly useful for high speed milling combined with ramp down operations.
It is still a further object of the present invention to provide a cutting insert that is particularly useful for high speed milling combined with ramp down operations that has an increased number of cutting edges.
It is yet a further object of the present invention to provide a tool for clamping such a cutting insert.